Ceramic materials are well known for their unique combination of properties such as high hardness and strength, corrosion and erosion resistance, and excellent high temperature properties. However, due to their low fracture toughness, their use to date has been limited to cases where fracture toughness is not the requirement.
The strive to increase fracture toughness has led to the development of various methods for toughening of ceramics. The most widely used method of toughening involves impregnating the matrix with fibres and sintering at high temperature to eliminate porosity. There are two major problems associated with this method. First the strong ceramic fibres used for reinforcement are relatively very expensive and their handling requires extreme care. Second, incorporation of fibres into ceramic matrix is relatively very complicated, making the entire process commercially uncompetitive, particularly for mass production.
Another method of toughening ceramics [Nature Vol.347, p.455 (1990), Proceedings of the 4th International Conference on Fibre Reinforced Composites, Edited by G. Gibson, Institute of Mechanical Engineering, pp.179, Liverpool, (1990)] involves creation of weak interfaces capable of deflecting the crack and thus changing the mode of fracture from Mode I to Mode II. The method consists of mixing the ceramic powder with 30 to 40% by volume of aqueous polymer solution, rolling the mix into thin laminae and subsequent pressureless sintering to achieve densification. The layer structure is produced by compacting together, in a green state, thin sheets of ceramics separated by thin graphite layers. The ceramic bodies produced with this method exhibit fracture toughness in excess of 17 MPa.m.sup.1/2. There are two major problems associated with this technique. First, the polymeric substance used in this process is difficult to mix with ceramic powder and thus requires special mixing equipment. Second, in order to avoid cracking of the green bodies, the removal of the polymeric binder is a very slow process, requiring long thermal cycles, normally days or even weeks.
It would be an improvement in the art if high toughness ceramic laminated structures can be produce without the use of polymeric component and employing simpler processing techniques such as slip casting.